The research involves several projects under each of the following headings: 1. Hemopoietic colony formation on macrophage-fibroblast coated membranes inserted intraperitoneally. 2. In vitro propagation of hemopoietic and lymphoid organ-stromal cells of the hemopoietic inducing microenvironments (HIM) and lymphoid inducing microenvironments (LIM). 3. Light and electron microscopic visualization of the stromal cell-stem cell interactions of the erythroid and granuloid HIM. 4. Role of HIM and LIM in leukemia-lymphoma. 5. Lymphoid inductive functions of the thymus.